Low-Temperature Sintering And Microwave Dielectric Properties Of Ba₂Ti₃Nb₄O₁₈ Ceramics

With the development of mobile communications and satellite communications, microwave dielectric ceramics are widely used as resonators, filters, waveguides, and so on. In order to fulfill the requirements of the miniaturization of microwave components, ceramics with high dielectric constant (εr), low loss microwave, and low sintering temperature should be developed. The Ba₂Ti₃Nb₄O₁₈ ceramics behaves excellent microwave dielectric properties such as highεr, high quanlity factor (Q·f), and low temperature coefficient of the resonant frequency (τf). However, its sintering temperature is too high, nearly 1300°C. It is essential to lower its sintering temperature.In this paper, Ba₂Ti₃Nb₄O₁₈ ceramics was prepared by the traditional solid state reaction route, and CuO and H₃BO₃ were used as sintering aids to lower its sintering temperature. The influence of CuO and H₃BO₃ addition on the sintering behaviour and microwave dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramics was investigated. The crystaline phase composition and microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. The dielectric properties of specimens were measured by parallel-plate resonator method.The results show that CuO can obviously promote the densification of Ba₂Ti₃Nb₄O₁₈ ceramics and decrease its sintering temperature. When the addition of CuO was less than 1.0 wt%, the density of the Ba₂Ti₃Nb₄O₁₈ ceramics remarkably increased with the increasing amount of CuO and reached a saturation value at 1.0 wt% addition of CuO. The addition of H₃BO₃ had a great influence on the densification of Ba₂Ti₃Nb₄O₁₈ ceramics when inadequate CuO (< 1.0 wt%) was added while a very weak influence when adequate CuO (≥1.0 wt%) was present in this ceramic system. Further, the Q·f value increased with the addition of H₃BO₃ and reached a maximum value when H₃BO₃ is up to 3.5 wt%. However excess H₃BO₃ addition, led to the formation of excess second phases and therefore the decrease in Q·f value.Appropriate addition of H₃BO₃ and CuO remarkably improved the microwave dielectric properties of ceramics. The addition of H₃BO₃ and CuO successfully reduced the sintering temperature of Ba₂Ti₃Nb₄O₁₈ ceramics from 1300 to 1050°C. Ba₂Ti₃Nb₄O₁₈ ceramics sintered at 1050°C for 4 h with the addition of 1.0 wt% CuO and 3.5 wt% H₃BO₃ exhibited good dielectric properties:εr = 33.74, Q·f = 13812 GHz, andτf = -5.35 ppm/°C.